Grafting of high and low molecular weight polymers has been reported often in the literature [see for example, polymer textbook "Polymer Chemistry" by M. P. Stevens, (Addison-Wesley), 1975, pp 196-202]. Maleation is a subgroup of grafting. Those skilled in the art recognize the highly individualistic nature of the maleation processes which have been patented. For example, direct maleation of polyethylenes results in cross-linking which increases the molecular weight of the polymer [see for example, "Journal of Applied Polymer Science", 44, 1941, N. G. Gaylord et al (1992); and U.S. Pat. Nos. 4,026,967, 4,028,436, 4,031,062, 4,071,494, 4,218,263, 4,315,863, 4,347,341, 4,358,564, 4,376,855, 4,506,056, 4,632,962, 4,780,228, 4,987,190, and 5,021,510]. Often free radical initiated maleation of polyethylenes is limited to very low acid numbers in order to prevent gelation due to excessive crosslinking. Thermal maleations without the use of initiators is also employed for maleation of polyethylenes in order to minimize crosslinking. Other techniques such as the addition of chain transfer agents or special reagents have been reported. On the other hand maleation of polypropylenes progresses easily with free radical initiation (see U.S. Pat. Nos. 3,414,551, 3,480,580, 3,481,910, 3,642,722, 3,746,676, 3,932,368, and 4,613,679). The molecular weight of the products of such reactions are lower than that of the starting polypropylene due to accompanying degradation reactions.
Different techniques of maleation yield different product types. Solid state maleations, those carried out below the melting point of the polymer, occur on the exposed surface of the solid. The acid numbers attained are necessarily a function of exposed surface area. Solvent based processes dissolve the polymer and produce a much more uniform maleated product [see U.S. Pat. Nos. 3,416,990, 3,437,550, 3,483,276, 3,928,687, 4,078,017, 4,299,754, 4,624,992, and 4,693,838 and Japanese Patents 59 105,053, 84 105,053 (1984), 69 15,422 (1969), 69 15,423 (1969), 77 93,495 (1977) , 80 34,224 (1980), and 82 42,736 (1982). Solvent removal and recycling is an added expense of such processes however. An extruder serves as the reactor in some processes and provides some decrease in the molecular weight of the polymer due to mechanical tearing of the polymer chains [see U.S. Pat. Nos. 3,862,265, 4,003,874, 4,548,993, 4,639,495, 4,751,270, 4,762,890, 4,857,600, 4,927,888, and 5,001,197 and Japanese Patents JP 63,309,540, 88,309,540 (1988) and JP 78,137,292 (1978 ) and European Patent Application EP 280454 (Aug. 31, 1988)]. Some other processes resort to other chemical reactions such as oxidation or reaction with an alcohol or amine, either before maleation or after maleation, to provide unique products [see U.S. Pat. Nos. 4,443,584 and 4,727,120 and Japanese Patent JP 77 08,035 (1975)]. In other processes copolymers are used to alter the molecular weight increases as in maleation of polyethylenes or the molecular weight decreases as in maleation of polypropylenes (see U.S. Pat. Nos. 3,953,541, 4,533,700, 4,612,155, 4,749,505, and 4,822,688). Finally, the processes which are carried out in water must involve maleation with a mixture of maleic acid and maleic anhydride at best, and possibly involve maleic acid exclusively (see U.S. Pat. Nos. 4,370,450, 4,839,423, 4,877,841, and 4,879,347). The product of these aqueous processes are necessarily the carboxylic acids rather than the anhydrides which are obtained in other maleation reactions.
Maleated polypropylene waxes and emulsions containing these waxes are known in the commercial field and to the chemical literature as disclosed above. The use of maleated polypropylene waxes in floor polish formulations to provide black heel mark protection is practiced. However, heretofore maleation of polypropylene waxes has provided products which gave semi-opaque emulsions. For example emulsions prepared from Epolene E43 (a maleated polypropylene wax from Eastman Chemical Company) typically exhibited less than 5.3% light transmittance (20 mm pathlength at 520 nm). This meant that use of these emulsions in floor polish formulations to provide better black heel mark resistance was limited to products which were less than completely clear. Maleated polypropylene waxes which provide higher clarity emulsions should yield an advantage in the clarity of the final floor polish which contain these waxes.
The melt viscosities of these maleated polypropylene products such as Epolene E43 were low, in the range of 200-400 cP at 190.degree. C. Amounts of these low melt viscosity maleated polypropylene waxes which could be incorporated into floor polish formulations were limited because large amounts gave final floor finishes with less than desirable toughness. The addition of other components to the floor polish formula was needed to compensate for the poor toughness of these maleated polypropylenes. Higher viscosity maleated polypropylenes would be advantageous in that less or no additives would be necessary to obtain the desired toughness in the final floor finish.
Attempts were made to increase the melt viscosity of products by the substitution of higher molecular weight/melt viscosity starting materials. However, maleated products having higher melt viscosities gave solids which could not be emulsified in that large amounts of solid were insoluble in the emulsion mixture. Even after filtration of the insoluble solids the emulsions remained opaque. Thus commercial use of these higher viscosity products was precluded.
In light of the above, it would be very desirable to be able to produce maleated polypropylene waxes that are emulsifiable and produce clear emulsions that result in tough floor finishes.